Devanathan-Stachurski or H cell is successfully used to the evaluation of hydrogen permeation in sheets or membranes. H cell consists of two electrochemical compartments separated by a sheet which acts as working electrode (WE) in both cells. This setup allows the generation of hydrogen in the charging cell, applying a controlled potential or constant current. It diffuses though the sample and is electrochemically detected in the oxidation compartment where the hydrogen gas is oxidized applying a constant potential [1]. The anodic current is directly proportional to the amount of hydrogen penetrating through the membrane with time. As small amounts of hydrogen pass through the membrane, a very sensitive potentiostat is required for its detection. In addition, since the two electrochemical cells use the same WE, two equipments with floating mode with galvanostatic isolation should be used.

Taking into account the instrumental requirements, the study of the hydrogen permeation properties of different iron sheets have been analyzed in this work. Different electrochemical profiles are obtained depending on the sample (Figure 1): sample 1 (red line) exhibits a larger diffusivity of the hydrogen due to the higher current recorded, while sample 2 (blue line) not only shows lower current but also shows a delay in the hydrogen transport due to its lower permeability. The absorption of hydrogen by ferrous metals is a serious problem because the hydrogen embrittlement can produce modifications of the mechanical properties of the material with occasional stress corrosion cracking.

Figure 1. Hydrogen transients obtained using two different iron samples.

References

[1] ASTM G148-97, “Standard Practice for Evaluation of Hydrogen Uptake, Permeation, and Transport in Metals by an Electrochemical Technique.”